1. Field of the Invention
The present invention relates to a part feeding apparatus which can perform a stable feedback control upon a feeding amount of parts such as semiconductor elements.
2. Description of the Related Art
For example, in a semiconductor element assembly apparatus, a part feeding apparatus for feeding parts which are, in this case, semiconductor elements has been combined therewith. In such a part feeding apparatus, it is important to stabilize the amount of parts fed to the assembly apparatus so that it is brought close to a definite value, to thereby suppress fluctuation of a rate of operation of the assembly apparatus.
A first prior art part feeding apparatus is constructed by a feeder bowl for discharging and feeding parts to the assembly apparatus, a feeder bowl driving unit, i.e., an electromagnetic oscillation applying unit, a sensor for detecting parts discharged from the feeder bowl, and a counter for counting the number of parts discharged from the feeder bowl. In this case, an oscillation amplitude of the electromagnetic oscillation applying unit is changed in accordance with a difference between the number of parts discharged from the feeder bowl per unit time and a definite value, so that the number of parts discharged from the feeder bowl is brought close to the definite value (see Japanese Unexamined Patent Publication (Kokai) No. Hei 2-231305). In this first prior art part feeding apparatus, however, since the oscillation amplitude of the electromagnetic oscillation applying unit is changed, this oscillation amplitude may be deviated from an optimum value, thus inviting fluctuation of the number of parts discharged from the feeder bowl. This will be explained later in detail.
A second prior art part feeding apparatus is constructed by a feeder bowl for discharging and feeding parts to the assembly apparatus, a feeder bowl driving unit, i.e., an electromagnetic oscillation applying unit, a sensor disposed within the feeder bowl, a hopper for discharging and feeding parts to the feeder bowl, and a hopper driving unit, i.e., an electromagnetic oscillation applying unit. In this case, the sensor detects whether or not the number of parts within the feeder bowl is smaller than a definite value. As a result, when the number of parts within the feeder bowl is smaller than the definite value, the hopper driving unit is turned ON to discharge and feed parts to the feeder bowl. Contrary to this, when the number of parts within the feeder bowl is not smaller than the definite value, the hopper driving unit is turned OFF to stop discharging and feeding parts to the feeder bowl. Thus, the amount of parts within the feeder bowl is brought close to the definite value. In this second prior art part feeding apparatus, however, since the sensor detects a top of parts within the feeder bowl which does not always correspond to the amount of parts within the feeder bowl, the amount of parts within the feeder bowl is not definite, and accordingly, the amount of feeding parts is not definite. This will be explained later in detail.
A third prior art part feeding apparatus includes a mechanical switch instead of the sensor of the second prior art part feeding apparatus. That is, the mechanical switch detects whether or not the weight of parts within the feeder bowl is less than a definite value. As a result, when the weight of parts within the feeder bowl is smaller than the definite value, the hopper driving unit is turned ON to discharge and feed parts to the feeder bowl. Contrary to this, when the weight of parts within the feeder bowl is not smaller than the definite value, the hopper driving unit is turned OFF to stop discharging and feeding of parts to the feeder bowl. Thus, the weight of parts within the feeder bowl is brought close to the definite value (see Japanese Unexamined Utility Model Publication (Kokai) No. Hei 2-64513). In this third prior art part feeding apparatus, however, when the weight per one part is changed, i.e., the kind of parts is changed, it is necessary to adjust the mechanical switch. This will be explained later in detail.